Alkanolamines, for example, triethanolamine, are widely used in cosmetic and pharmaceutical products such as soaps, cleaners, and shampoos. One problem associated with the use of alkanolamines is discoloration. That is, during storage, the color of alkanolamines deepens, making them unsatisfactory for certain applications.
Methods for improving color stability of alkanolamines are known. For instance, U.S. Pat. No. 6,323,371 discloses the preparation of alkanolamines having improved color quality by treating the alkanolamines with phosphorous acid or hypophosphorous acid prior to distillation. The pretreatment, although producing alkanolamines having low fresh color, does not effectively prevent the discoloration during the product storage.
U.S. Pat. No. 3,207,790 describes a process for improving the color quality of alkanolamines by the addition of alkali metal borohydride to the alkanolamines. However, the addition of alkali metal borohydride does not produce satisfactory results.
New improvement for the color stability of alkanolamines is needed. Ideally, the alkanolamines would remain on-the-spec color (APHA color less than 50) for at least 3 months at room temperature.